1. Field of the Invention
This invention relates to a method for manufacturing a lapping tool to be used for grinding or polishing glasses such as optical lenses, and so on. More particularly, it is concerned with the manufacture of the lapping tool, in which small pieces of plastic sheets, or pellets, are adhered onto the surface of a cast iron dish, etc.
2. Description of the Prior Art
Heretofore, lapping of an optical lens has been performed in such a way that the lens is first subjected to a grinding work by means of a lapping dish produced by adhering diamond pellets onto the surface of a cast iron tool, and subsequently to polishing work by means of a polishing tool produced by adhering pitch or a plastic sheet for polishing onto the surface of the cast iron tool, while a polishing liquid [an aqueous solution of cerium oxide (CeO.sub.2) or zirconium oxide (ZrO.sub.2)] in the main is being fed into a sliding surface between the lens and the polishing dish.
The polishing tool to be used for the above-mentioned purpose has heretofore been manufactured in the following manner. A foam controlling agent is first added to liquid polyurethane elastomer, and the batch is agitated at a high speed with addition, if necessary, of cerium oxide (CeO.sub.2) or zirconium oxide. Subsequently, a hardening agent molten at 120.degree. C is added to this elastomer and mixed uniformly, followed by heating at a temperature of 100.degree. C, to obtain foamed polyurethane in block shape. Then, this foamed polyurethane block is cut into a sheet of an appropriate thickness, after which the sheet is cut into pellets of a desired sheet. The pellets are then adhered onto the surface of a cast iron tool body, etc. by an adhesive agent to produce the complete lapping tool.
In the conventional method of manufacturing the lapping tool as described in the preceding, a considerably long time is required for the complete preparation of the lapping tool. That is to say, the number of the pellets to be adhered onto the lapping tool often amounts to from 70 to 200 pieces, the accurate adhesion of which onto the lapping dish necessitates considerable time and skill. Further, since the pellet surface is flat, while the surface of the lapping tool is curved, a greater quantity of the adhesive agent is required to be used for the pellets for complete adhesion on the curved tool surface, which has presented a problem. Furthermore, since the pellet-adhered lapping tool as so made does not always same have the surface curvature as that of the lens to be made, it has been unavoidable that the curvature of each lapping tool has had to be checked and corrected by a curvature correcting tool.